Vibrating gyroscope

ABSTRACT

The invention relates to a vibrating gyroscope comprising vibrating cylinder ( 1 ) that is magnetically or electrostatically excited. Regularly distributed masses ( 19 ) designed to lower the vibration frequency of said cylinder are arranged thereon. The inventive gyroscope is much more accurate than conventional gyroscopes and can be produced easily at low cost. The invention can be used to measure angular rotation or angular speed.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention concerns a vibrating gyroscope for accuratelymeasuring angular rotations. Compared with the techniques generallyused, this gyroscope proves to be more effective, occupies less space,is simple to embody and is less expensive.

2. Description of the Invention

Vibrating gyroscopes are based on the effect of Coriolis forces due to arotation imposed on moving masses.

Several embodiments have been previously proposed for embodying avibrating element sensitive to angular speeds.

The method most frequently used consists of making an annular,hemispherical or cylindrical test body of revolution vibrateperpendicular to its axis of symmetry and of observing the movement ofthe vibration modes when it is subjected to rotation around said axis.

In the most general case of annular, hemispherical or cylindrical testbodies, the main difficulty derives from the compromise that has to bemade between the resonance frequency which increases with the spatialrequirement reduction and the time constant which determines theperformance and which is improved when the resonance frequency is low.For example, it is virtually impossible to embody a cylindrical testbody having a thin wall, a volume smaller than 2 cm3 and a resonancefrequency lower than 6 kHz. Now it would be desirable to have small testbodies resonating only between 2 and 3 kHz so as to obtain much improvedperformances.

The second difficulty originates from the embodiment of the excitationand vibration measuring device, it being understood that the term‘excitation’ denotes all the commands required for the properfunctioning of these gyroscopes.

Solution put forward to date for creating, detecting and maintainingvibration are basically of the electromagnetic, electrostatic orpiezo-electric types.

The electrostatic solutions have advantageous performances when they areused under vacuum so as to reduce losses. Because they require extremelysmall air gaps, they are difficult to implement inside or outside ahemispherical or cylindrical wall and are thus generally expensive.

The piezo-electric solutions use either a cylinder made fully of apiezo-electric material, or small piezo-electric elements mounted, mostfrequently by glueing, on a metal cylinder. The solutions have one majordrawback when used in gyrometric applications for which they arebasically adapted of being unable to adjust the axis of excitation withrespect to the vibrating body which generally has one overridingdirection for which performances are optimum.

For various reasons and in particular for reasons of cross talk, themeans for detecting and exciting the vibrations of certain embodiments,are heterogeneous and are spaced as far a s possible from one another.

For example, the U.S. Pat. No. 4,793,195 describes a gyrometer with avibrating cylinder provided with electrostatic detection andmagnetically excited at a frequency half its vibration frequency so asto reduce these effects.

The French patent application 97/12129 describes a gyrometer withmultiplexed magnetic detection and excitation which clearly resolves thedifficulty of crosstalk between excitation and detection but whoseperformances are limited by Vie resonance frequency which remains high.

OBJECT OF THE INVENTION

The present invention brings about an improvement which, in a givenspatial requirement, makes it possible to choose the resonance frequencyand via its principle offers new possibilities for simply and cheaplyembodying electromagnetic or electrostatic detection and excitationmeans.

So as to reach this result, the thin-walled test body of revolutioncomprises at its periphery evenly distributed masses separated byintervals which increase the moving mass when said test body is excitedon vibration Openings can be fitted in the thin wall of the cylinder andnot covered by the masses so as to adjust the stiffness of the end ofthese masses and thus the resonance frequency. This makes it possible tosignificantly reduce the resonance frequency of said test body and thusincrease performances.

By acting on the shape of the openings, it is possible to favour certaintypes of movements of additional masses and thus embodying inexpensiveflat electrostatic or magnetic detection/excitation units able to beplaced at the right of a flat open extremity of the test body and thusextremely easy to adjust.

SUMMARY OF THE INVENTION

Thus, the invention concerns a vibrating gyroscope of the typecomprising:

a thin and vibrating element and approximately generated by rotation,

excitation means for generating vibrations at least one point of thevibrating element so as to make appear on said vibrating elementvibration modes able to be modified under the effect of an angular speedof rotation, and

means for detecting said vibrations and arranged so as to be able todetect said vibration modes,

characterised in that the vibrating element approximately generated byrotation at receives at least three and preferably eight masses formingvibrating masses and preferably constituted by excessive thicknesses ofthe vibrating element itself.

BRIEF DESCRIPTION OF THE DRAWINGS

There follows hereafter non-restrictive embodiments of the inventiongiven solely by way of example with reference to the accompanyingdrawings on which:

FIG. 1 is a skeleton diagram showing the functioning of a vibratinggyroscope,

FIG. 2 is a cutaway side view of the vibrating gyroscope of theinvention,

FIG. 3 is an axial cutaway view showing the vibrating gyroscope of FIG.2 along the direction A,

FIG. 4 is a cutaway side view of the vibrating gyroscope of FIG. 2 in avariant with excitation and electrostatic detection,

FIG. 5 shows two views of a variant of the test body of the vibratinggyroscope of FIG. 2,

FIG. 6 is a cutaway side view of the variant of the test body of FIG. 5,

FIG. 7 shows two views of a preferred variant of the test body of thevibrating gyroscope of FIG. 2,

FIG. 8 is a cutaway side view of the variant of the test body of FIG. 7,

FIG. 9 is a cutaway side view of a variant of the gyroscope of FIG. 2using the test body of FIG. 7 and a flat electromagneticexcitation/detection unit,

FIG. 10 is an axial cutaway view of the variant of the gyroscope of FIG.9 along the direction A,

FIG. 11 is a cutaway side view of a variant of the gyroscope of FIG. 9and using a flat electrostatic excitation/detection unit, and

FIG. 12 is a skeleton diagram of the electric and electronic circuits ofthe vibrating gyroscope of the invention in the multiplexing versionwith excitation and detection functions adapted to the electrostaticdetection and excitation gyroscopes of FIGS. 4 and 11.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As previously mentioned and shown on FIG. 1, a vibrating gyroscopecomprises a test body 1, having an axis of symmetry 6, cylindrical forexample (FIG. 1a) but which can be hemispherical or have any other shapeof revolution, and which is excited on vibration (FIG. 1b) along twoinitial directions 2 and 3 perpendicular to each other and to the axis 6of the test body 1 so that four nodes 4 and four vibration antinodes 5appear, the movements of the portions situated on the vibrationantinodes being in phase opposition for the two initial excitationdirections 2 and 3.

When the test body 1 is subjected to an angular speed rotation Ω aroundan axis parallel to the axis of symmetry 6, the vibration nodes do notrotate with the test body. They no longer remain fixed in space but theyrotate with respect to the inertial space at an angular speed ω=K.Ωwhich depends on the geometry and angular speed of the test body. Thetheoretical ratio K between the angular speed of the test body and thatof the vibration nodes also depends on the vibration mode. For example,it is possible to make the test body vibrate with six vibration nodesand six vibration antinodes, but the corresponding configuration is lessfavourable for the gyroscopic measurement.

Thus, the vibration nodes 4 are not linked to the test body 1, but movewith respect to the latter with an angular speed, also proportional tothe angular speed of the test body itself.

FIG. 2 shows a cutaway view of a preferred embodiment of the vibratinggyroscope of the invention.

This comprises:

a test body or vibrating cylinder 1,

a support 7,

an external cylindrical box 8,

a magnetic detector exciter or stator 9,

an electronic circuit 10,

fixing, cabling and closing means.

The test body is embodied in the form of an approximately cylindrical.vibrating element or vibrating cylinder 1 having an axis of symmetry 6,a wall 11 open at one of its extremities 12 and closed at its otherextremity 13 by a wall forming a bottom 14. The wall 11 of the vibratingcylinder 1 is thin and regular on one portion of its length 15 close tothe bottom 14. Said bottom comprises an external portion 16 havingapproximately the same thickness as that of the wall 11 of the cylinderand at the centre a thicker portion 17.

The wall 11 of the vibrating cylinder bears on one portion of its height18 close to its open extremity 12 at least three and preferably eightexcess thicknesses or masses 19 evenly distributed and whose shape canbe any. In one preferred embodiment of the invention, the height ofthese excess thicknesses 19 is parallel to the axis of symmetry 6 of thetest body and approximately equal to half the total height of said testbody. Their section as shown on FIG. 3 perpendicular to the axis ofsymmetry 6 is externally bordered by an arc of a circle 20 centred onsaid axis of symmetry 6. It is bordered on the sides by two blanks 21and 22 parallel to said axis of symmetry and orientated so that oneblank 21 with an excess thickness 23 is parallel to one immediatelyadjacent blank 22 with an excess thickness 24. This arrangementfacilitates machining of said excess thicknesses by means of milling.

The bottom 14 is fixed at its centre onto the support 7 by an internalfoot 25.

The support of revolution 7 comprises a first portion 26 whose diameteris such that it is able to receive the external box 8, and a secondportion comprising two successive decreasing diameters 27 and 28, thesecond diameter being used to act firstly as a support for the magneticstator 9 on which coils 30 are placed, and secondly as a support for thevibrating cylinder 1.

It is dimensioned so that the stator 9 is placed centred in the openextremity 12 of the vibrating cylinder 1 thus providing an air gap 29having a thickness reduced as far as possible.

The magnetic exciter is embodied in the form of an eight-branched star31 and thus comprises eight poles 32 on which the coils 30 are placed.

As described above, the gyroscope of the invention functions as followsby first of all making the hypothesis that the losses are nil and thatthe vibrations once established conserve their energy. The vibrationsare initially created on two pairs of masses 23, 33 and 34, 35 forexample placed on two perpendicular axes 3 and 2, the other four masses36 to 39 not vibrating. In the absence of rotation, the vibrating statedoes not change. In the presence of a rotation Ω around the axis 6, theeffect of the Coriolis forces results in a transfer of energy of themasses which initially vibrated towards the latter which did not vibrateso that the total energy is retained. If A is the initial peak amplitudeof the vibrations of the two pairs of masses 23, 33 and 34, 35, the peakamplitude of these vibrations at the end of a time t is written:

A=A.cos[2(1−K), fΩ.dte].

Similarly, the peak amplitude of the vibrations of the four other masses36, 37 and 38, 39 is written:

B=A.sin[2(1−K), fΩ.dte].

Because the losses by rubbing in the material are not nil, thevibrations tend to dampen and need to be maintained so as to ensurefunctioning of the gyroscope.

To this effect, by using the well known principles of electroniccircuits, the amplitudes of the vibrations of each of the 4 pairs ofmasses are measured and are used to draw up holding and correctionvoltages which are sent to the windings. Advantageously, the principlesfor multiplexing excitation and detection described in the French patentapplication no 97/12129 shall be used

For a gyrometer usage, again using the well-known principles ofcounter-reaction and preferably the multiplexing technique, the fourmasses 36, 37, 38 and 39 are kept immobile by sending to thecorresponding windings a counter-reaction voltage opposing the effectsof the Coriolis forces. This counter-reaction voltage is thenrepresentative of the angular speed Ω. The vibration amplitude of themasses 23, 33, 34 and 35 is kept constant.

Thus as shown on FIG. 4, the electromagnetic detection/excitation unit 9can be replaced by an electrostatic detection/excitation unit 40. Tothis effect, the stator 9 of FIG. 2 is replaced by a ring 41 made of anon-conducting material with at least two and preferably eight or moreelectrodes 42 being placed on the periphery of said ring. The outerdiameter of this ring is such that the electrodes are found opposite theinternal face of the cylinder 1 with an air gap 29 reduced as much aspossible.

So as to improve the performances of the vibrating gyroscope, it may benecessary to reduce the stiffness provided by the thin portion of thevibrating cylinder. As shown on FIG. 5, one first variant of theinvention consists of embodying in the thin wall 11 of the vibratingcylinder openings 43, said openings being evenly distributed and centredapproximately between the masses 19. Seen from the side, FIG. 5a shows avibrating cylinder pierced with eight relatively fine long openings 43whose largest dimension is approximately parallel to the axis 6. Theseopenings preferably go down as far as the thin portion 16 of the bottom14 of the vibrating cylinder. At their other extremity, they may becloser or further away from the upper portion of the thin wall 11 of thecylinder remaining between the masses, the thin wall portion remainingbetween said openings 43 and the extremity 12 of the cylinderconstituting the elastic bridges 79 between the masses 19. Moreover inthe example shown, the height and position of the additional masses aresuch that the latter go past the height of the cylinder itself, thusforming notches on the side of the open extremity 12 of said cylinder 1.

FIG. 6, which is a cutaway view of the vibrating cylinder describedabove, shows, by exaggerating it with respect to reality, the movementof two of the masses 19 under the effect of the vibrations. Because ofthe shapes retained and the position of the openings, it appears thatthe masses 19 on vibrating carry out a rotation movement approximatelycentred at a point 44 corresponding to the joining point between theextremity 13 of the cylinder 1 and the flat thin wall 16. If oneconsiders the movement from an upper corner 45 of the mass 19, thisdrawing shows that under the effect of this rotation that the upperportion of the masses and in particular the point 45 is moved firstly bya translation movement perpendicular to the axis 6, and secondly by atranslation movement 50 parallel to said axis 6 but with a much morereduced amplitude.

Still with the aim of improving the performances by adjusting as best aspossible the rigidities and the masses, it is possible to extend theopenings 43 made in the wall 11 of the vibrating cylinder 1 onto thebottom 14 in the direction of the foot 25. FIG. 7 is divided into FIG.7a and 7 b, the first being a side view of the test body and the other atop view of said body. The openings 43 are extended by grooves 46,preferably radial, on the bottom 14. These grooves 46 are preferablynarrowed towards the centre and the masses 19 are therefore connected tothe centre by a cylindrical wall portion 47 and by a flat sector 48perpendicular to said cylindrical wall portion 47, said flat sectorcomprising a narrowing 49 close to the centre.

In addition, the openings 43 are extended on the wall 11 between themasses 19 in the direction of the extremity 12 of the vibrating cylinder1 so that the remaining portion of said wall 11 between, said masses 19is approximately reduced and constitutes an elastic bridge 79 betweenthese masses.

Because of the narrowing 49 and the elongation towards the extremity 12of the openings 43, the most flexible portion of the link between themasses and the centre is located exactly at the location of thisnarrowing 49. Thus, as shown on FIG. 8, the hinge point 44 of themovement of the masses 19, which is located approximately at this mostflexible location, is thus much closer to the axis 6 than that of thepreceding variant of FIG. 6. FIG. 8 also shows the movement of themasses 19 in the configuration of FIG. 7. It appears that thetranslation movement 50 parallel to the axis 6 from the corner 45 ismuch larger and it can also be used to excite and detect the vibrationswith an excitation/detection system having a flat interface with thevibrating element, said interface being constituted by air gaps 29, asshown on FIG. 9. In this configuration, the shape of the elastic bridges79 is determined so as to harmonise the various rigidities and avoidcreating parasitic resonance frequencies too close to the nominalfrequency of the test body.

FIG. 9 thus shows a cutaway view of a first example of the gyroscopeusing this translation movement parallel to the axis 6 with anelectromagnetic excitation/detection system having along with thevibrating element an interface of revolution 83 centred on the axis 6and preferably flat. The masses 19 having a section perpendicular to thelarge axis 6 can be embodied with one extremity or face 51 situated onthe side of the open portion 12 of the vibrating cylinder, said sectionbeing flat and thus able to be used with a simple electromagnet, thefaces 51 of each of the masses 19 being approximately coplanar.

The detection/excitation unit then includes at least two, but preferablyeight electromagnets 52 secured to the support 7 and whose magneticcores 53 each have one flat extremity 54. Said flat extremities 54 arecoplanar between one another and each extremity is placed opposite aflat extremity 51 from one of the masses 19 with an air gap 29 reducedas much as possible, the air gaps 29 forming the interface 83.

It is to be noted that the interface 83 could be slightly conical oreven spherical or more generally have a not fully flat shape withoutdeparting from the context of the invention.

So as to be more effective by reducing losses, each of theelectromagnets may include, as shown on FIG. 10, two short cores 53having axes approximately parallel to the axis 6, each core preferablybeing placed at an equal distance from said axis 6, said cores beinginterconnected, preferably two by two, by a magnetic reinforcement 55secured to the support 7 opposite the flat face 51 of the rings 19. Awinding 56 is placed around each of these cores 53. So as to furtherreduce the magnetic losses, a plate 57 made of a low loss magneticmaterial and preferably having the same surface as the section of themasses 19, is secured to each flat face 51 of said masses and via theair gap 29 close a magnetic circuit constituted by a pair of cores 53and their reinforcement 55. The outer face of the magnetic plate thenconstitutes the flat face 51.

In this configuration as in the configuration of FIG. 4, the gyroscopemay advantageously use the multiplexing technique described in theFrench patent application no 97/12129. It can also be used as agyroscope or a gyrometer.

The vibrating cylinder of FIG. 7 is also clearly suitable in the use ofan electrostatic flat interface detection/excitation system, as shown onFIG. 11 showing also a gyroscope equipped with this system. This systemcomprises a non-conducting crown 58 secured to the support 7 oppositethe flat faces 51 of the masses 19. Secured to this crown are at leastand preferably eight electrodes 59, each electrode being placed oppositeone of the faces 51 of said masses 19.

The vibrating cylinder is positioned on the support so that the air gap29 between the electrodes and the faces 51 constituting the interface 83is as reduced as possible.

This latter variant preferably uses one multiplexed electronics unitwhose principle is shown on the diagram of FIG. 12 and which avoids anyproblem of crosstalk between the excitation signals and the detectionsignals.

In this solution, the electrodes 59 are in turn used to excite and thendetect the vibrations of each of the masses, knowing that it is alsopossible to use one portion of the electrodes for detection and use theothers for excitation.

The electrodes are connected by pairs, the electrodes of a given pairbeing placed symmetrically with respect to the axis 6.

The faces 51 of the electrically interconnected masses 19 form acounter-electrode 77 fed by a circuit 78.

Each of the pairs of electrodes is connected to a circuit changer 89,80, 81, 82 and controlled by a sequencer 60. When the circuit changersare in the position B, the system functions in detection mode. When theyare in the position C, they function in the excitation mode.

In the detection mode, the signal derived from the pairs of electrodesfirstly respectively 61, 65 and 63, 67 and secondly 62, 61 and 64, 68are sent by means of two differential amplifiers 69 and 70 respectivelyto a calculation circuit 71 which works out on four outlets 73, 74 and75, 76 respectively four excitation voltages two by two in antiphasesent to the pairs of electrodes by means of the circuit changers whenthe latter move into the excitation position C.

The calculation circuit 71 works out the excitation frequency so thatthe latter corresponds to the resonance frequency of the masses of thevibrating cylinder.

The circuit 71 works out outgoing information 72 which represents the,rotation fΩ.dt of the gyroscope.

The sequencer 60 is synchronised by the excitation frequency with theaid of a signal derived from the calculation circuit 71.

The calculation circuit also makes the corrections required to theerrors brought about by the residual resonance deviations existingbetween the two vibration modes situated 45° from each another.

In a gyrometer use mode, the calculation circuit controls the vibrationof the masses situated opposite the electrodes 62, 66 and 64, 68 to benil, both in phase and in quadrature and thus compensate the resonancedeviations.

The operating frequency of the sequencer 60 is a sub-multiple of theactual frequency of the vibrating cylinder 1. The cyclic ratio ofswitching between the excitation time and the detection time may be 1/1.It can also advantageously be 1/2, 1/3, 1/4 or even lower, thisdepending on the excess voltage of said vibrating cylinder. Theswitchings of the excitation function to the detection function arepreferably carried out at the time when the voltage on the electrodes 61to 68 moves to zero. The switchings of the detection, function to theexcitation function are preferably carried out at the time the voltagecontrol sine wave in said electrodes moves to zero.

So as to obtain better distribution of the various resonance modes ofthe vibrating element, it is possible to replace all or part of thecylindrical wall 11 and the bottom 14 of the vibrating cylinder by acurved surface and apply to this new element all the arrangements andimprovements described above, this new vibrating element then having forexample a hemispherical, ellipsoid, parabolic shape etc., withoutdeparting from the context of the invention.

Finally, the use of additional masses can also be applied to aring-shaped vibrating element without departing from the context of theinvention.

What is claimed is:
 1. Vibrating gyroscope comprising: a thin wallhollow vibrating cylindrical element having a bottom, a foot centered onsaid bottom, an open extremity, and at least eight vibrating massesspaced evenly on said element and located close to said open extremitysaid masses forming excess thickness on said vibrating element so as toobtain a reduced resonance frequency of said vibrating element, saidvibrating element further comprising excitation means for generatingvibrations on at least one point of the vibrating element so as to haveappear on said vibrating element vibration modes able to be modifiedunder the effect of an angular rotation speed, and means for detectingsaid vibrations and placed so as to be able to detect said vibrationmodes.
 2. Vibrating gyroscope according to claim 1, wherein saidvibrating element comprises openings evenly spaced and centredapproximately between said masses.
 3. Vibrating gyroscope according toclaim 2, wherein the shape of the openings is elongated, their largestdimension being approximately parallel to the axis.
 4. Vibratinggyroscope according to claim 3, wherein said openings made in said thinwall of said vibrating cylinder are extended on the bottom of saidvibrating cylinder by notches, radial and narrowed towards said foot. 5.Vibrating gyroscope according to claim 4, wherein said masses each has asurface situated on a surface of revolution centred on the axis and arcflat, said surface of revolution constituting an interface for a systemfor exciting and detecting vibrations.
 6. Vibrating gyroscope accordingto claim 5, comprising a detection/excitation unit having a flatinterface approximately generated by rotation centred on the axisconstituted by at least two electromagnets secured to a support each ofsaid electromagnets having two magnetic cores interconnected by amagnetic reinforcement and placed opposite the faces of the masses, soas to form a magnetic circuit closed via an air gap constituting theinterface by a magnetic plate secured to the face of each of the masses.7. Vibrating gyroscope according to claim 4, comprising adetection/excitation unit having, together with the vibrating element, aflat interface approximately generated by rotation centred on the axisconstituted by at least two electrodes secured to a non-conducting crownsecured to a support and placed opposite the faces of the masses andseparated from said masses by an air gap constituting the interface. 8.Vibrating gyroscope according to claim 3, wherein the openings made inthe wall of said vibrating cylinder are extended between the massestowards said extremity of the vibrating cylinder so that the remainingportion of the wall between said masses is approximately reduced andconstitutes an elastic bridge between said masses.
 9. Vibratinggyroscope according to claim 1, comprising an electrostaticdetection/excitation unit including at least two electrodes connected tomeans for alternatively providing excitation and detection functions ofvibration movements of the vibrating element.
 10. Vibrating gyroscopeaccording to claim 9, comprising eight electrodes connected to saidmeans for alternatively providing the excitation and detection functionsof vibration movements of the vibrating element.